1) Field of the Invention
This invention relates to vehicle trailing arm air suspension system, more particularly to driven axles. Driven axles of trucks carry invariably an input shaft also called pinion shaft to which is connected a propeller shaft to transmit power from engine to differential assembly from where power is distributed to wheels on either sides of axle. A cardan type universal joint generally joins propeller shaft to pinion shaft. Angle of pinion shaft is set in a truck around an ideal design angle to achieve low included angle, called ‘joint working angle’, between propeller shaft axis and pinion shaft axis. During rotary power transmission from propeller shaft to pinion shaft, a low included angle will induce low rotational variation of pinion shaft that will in turn reduce inertial vibrations excited in the driveline system. Maintaining angle of pinion shaft axis around its set ideal design angle in various axle positions of jounce and rebound is a challenge when the trailing arm is clamped to axle. Change in pinion shaft axis angle from its ideal design angle will increase driveline induced vibrations in vehicle and also reduce life of driveline components. A substantially constant pinion shaft angle maintained around ideal design angle would result in low universal joint induced vibrations and longer life of parts in driveline.
During vehicle acceleration, coasting deceleration, and braking, a driven axle is subjected to equal and opposite torsional reactions, about axle lateral axis also called wheel axis, in response to drive torque and braking torque. Torsional resilience, about axle lateral axis, is generally incorporated in suspension systems. In a suspension where a trailing arm is “rigidly” clamped to axle, due to this torsional resilience, reaction torque on axle changes pinion shaft angle unless this reaction torque is suitably countered. A wide variety of prior art suspensions with objective of countering the reactive torque on axle based on four bar mechanism have been proposed and are examined in the following paragraphs.
2) Description of Related Art
In U.S. Pat. No. 7,168,718, Bjorn O. Svartz discloses a suspension where joint between lower control arm and axle is a pivot joint 31. All numbers in this paragraph refer to numbers used by Bjorn O. Svartz in U.S. Pat. No. 7,168,718 and has no equivalent relationship to invention disclosed herewith. He states in column 5 line 38 to 40, “The lower control arm passes under and is clamped to the rigid axle 6 by means of a pair of U-shaped clamps 27, 28.” Since lower control arm is ‘clamped’ to rigid axle the pivot 31 will be an additional connection to axle making the pivoting action redundant. This would make the arrangement a rectangular structure of four links 21-31, 31-42, 42-43 and 43-21 than a mechanism. Even if some assistance is drawn from resilient bushes in joints, the suspension would lack sufficient travel of axle because of clamping lower control arm to rigid axle. As will be understood by those skilled in the art, in a trailing arm suspension, wherein axle is connected to trailing arm around its mid length and arm ends connected to frame either directly or through an air spring, the trailing arm can be equated to a simply supported beam. Substantially concentrated upward load is applied to trailing arm at axle connection while frame rail connections exert downward load. In such a beam, maximum bending moment occurs around the point of upward force application. Corresponding stress on the beam due to this bending moment will need to be borne by material around upward force application point. In a control arm like that of 20, material around load application point 31 experiences maximum bending moment. Having a through hole at this point in a trailing arm would weaken the region around the through hole. This is primarily because a pivot joint like 31 needs a through hole in the trailing arm to receive pin or bush to be connected to axle.
In his U.S. Pat. No. 4,132,433, Willetts proposes a vehicle suspension wherein a trailing arm, mentioned as longitudinally-extending beam member 420, is connected to a rigid axle by a pivot joint as seen in his FIG. 2 and FIG. 3. To accommodate this pivot and outer sleeve 452, the trailing arm has a through hole as shown in his FIG. 3. This hole in trailing arm has the disadvantage of weakening the section of beam around the pivot joint.
Dudding et al. proposes a non-reactive trailing arm air suspension via U.S. Pat. No. 6,945,548 that has a pivot joint between trailing arm and axle. The trailing arm has a through bore at pivot joint 36 between trailing arm and axle where the highest bending moment would be experienced by the trailing arm.
Another feature generally found in prior art non-reactive trailing arm air suspensions that have a pivoted trailing arm front end is, the portion of trailing arm between front pivot and axle joint is vertically non-resilient. While air spring and shock absorber, which are generally disposed rearward of axle in such a trailing arm air suspension of a driven axle, substantially absorb shocks and energy by way of work done at the rear end of trailing arm, not enough energy is absorbed in suspension portion forward of axle. Elastomeric bushing in the front pivot absorbs very marginal energy as negligible work is done at that pivot. The joint between trailing arm and frame hanger bracket invariably experiences shocks that are transmitted to suspended mass causing occupant discomfort and requiring additional measures to counter negative effects of shocks on suspended mass.
In U.S. Pat. No. 6,390,485, Robert L. Caden describes a trailing arm air suspension wherein trailing arm is connected to axle by a pivot joint 56 that is outside the trailing arm body which is desirable as the trailing arm does not have a through hole. This also has the advantage of absorbing shocks both forward and rearward of axle. Robert achieves the non-torque reactive aspect of suspension by a mechanism built by an upper torque rod 74 for first link, a combination of frame and hanger bracket for the second link, a lower torque rod for the third link and axle for the fourth link. The torque rods 74 and its associated mounting brackets can be avoided if the front portion of trailing arm is made to function as a link that counters reaction torque.
Therefore in a non-torque reactive trailing arm suspension, it is desirable not to have a through hole in the trailing arm around the area where trailing arm connects to axle, to avoid structural weakening of trailing arm.
It is further advantageous to have a non-torque reactive trailing arm air suspension wherein substantial energy absorption takes place forward of axle by the trailing arm which trailing arm portion between axle joint and hanger bracket joint functions as one link of a four links mechanism, which mechanism achieves non-torque reactive aspect of suspension.
One of the objectives of this invention is to provide a non-torque reactive trailing arm air suspension wherein is provided a trailing arm which mid-portion that is connected to axle does not have a through hole as a means for connecting to axle.
Another objective of this disclosure is to provide a non-torque reactive trailing arm air suspension that is based on four bar mechanism that uses a spherical joint between axle and trailing arm, which spherical joint acts as one of four nodes of four bar mechanism and which spherical joint does not require the trailing arm to have a through hole.
Yet another objective of this invention is to provide a non-torque reactive trailing arm air suspension that uses a rolled and formed trailing arm which trailing arm first end is connected to hanger bracket by a pivot joint and uses the length of rolled and formed trailing arm between hanger bracket pivot joint and trailing arm axle joint as one of four links of four bar mechanism, which link portion has a partial length of trailing arm that is vertically resilient.
A ‘torque reactive’ trailing arm air suspension functionally attached to a driven axle has a pair of trailing arm assemblies, comprising pairs of hanger brackets, trailing arms, their attachments to axle and hanger brackets, air springs and shock absorbers. Front end of trailing arm of each assembly is generally pivotally connected to hanger bracket or longitudinally sliding and vertically restrained in hanger brackets. In the version of longitudinally sliding front end of trailing arm, the axle is connected to hanger bracket generally by additional tie link between axle and hanger bracket. This additional tie link is generally pivotally connected to hanger bracket and axle. Middle portion of trailing arm is generally “rigidly” clamped to one side of axle or pivotally connected to axle. The trailing arm generally extends behind axle where it is connected to one end of an air spring and to one end of a shock absorber. Other ends of air spring and shock absorber are connected to frame rail. Front portion of trailing arm bears partial suspended weight of vehicle. Rear portion of trailing arm bears partial suspended weight of vehicle through the air spring that is connected to frame rail. Rigidly clamped attachment of trailing arms to axle combined with pivoted or vertically-restrained-sliding of front end of trailing arm in the hanger bracket makes the suspension inherently reactive to torque induced by traction force and wheel braking torque. Due to resilience in the suspension system, this reaction on axle changes pinion shaft angle of driven axle. Effect of reaction on axle is more pronounced during vehicle acceleration from stop and during vehicle hard braking. While it is an industry practice to set angle of pinion shaft to its ideal design angle that substantially cancels joint working angle of all cardan joints in driveline system, a ‘rigidly axle mounted trailing arm set up’ generally does not maintain factory set pinion shaft angle during jounce and rebound of axle and during acceleration and braking.
In prior an ‘torque reactive’ trailing arm air suspensions where the trailing arm is rigidly clamped to axle, structural strength of trailing arm is preserved but the suspension is rendered ‘torque reactive’. In prior art ‘non-torque reactive’ a trailing arm air suspensions where the trailing arm uses a through hole as a means of pivotally connecting trailing arm to axle, the region around the hole experiences substantially high bending stress and the presence of through hole around that area further weakens the structure. In prior art non-torque reactive trailing arm air suspensions where the trailing arm does not have through hole but pivotally connects trailing arm to axle, an additional link and its mounting brackets are required to make a non-torque reactive suspension.